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Check if the memory is backed by a SAB by checking the constructor name #381

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Merged
merged 2 commits into from
Jul 3, 2025
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Merged

Check if the memory is backed by a SAB by checking the constructor name #381

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9b87015
make regenerate_swiftpm_resources
kateinoigakukun Jul 3, 2025
1993735
Check if the memory is backed by a SAB by checking the constructor name
kateinoigakukun Jul 3, 2025
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12 changes: 9 additions & 3 deletions Plugins/PackageToJS/Templates/runtime.mjs
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Original file line number Diff line number Diff line change
Expand Up @@ -308,7 +308,12 @@ class SwiftRuntime {
// Cache the DataView as it's not a cheap operation
let cachedDataView = new DataView(wasmMemory.buffer);
let cachedUint8Array = new Uint8Array(wasmMemory.buffer);
if (typeof SharedArrayBuffer !== "undefined" && wasmMemory.buffer instanceof SharedArrayBuffer) {
// Check the constructor name of the buffer to determine if it's backed by a SharedArrayBuffer.
// We can't reference SharedArrayBuffer directly here because:
// 1. It may not be available in the global scope if the context is not cross-origin isolated.
// 2. The underlying buffer may be still backed by SAB even if the context is not cross-origin
// isolated (e.g. localhost on Chrome on Android).
if (Object.getPrototypeOf(wasmMemory.buffer).constructor.name === "SharedArrayBuffer") {
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Copilot AI Jul 3, 2025

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Same here: using constructor.name may be brittle under minification or prototype mutation. A stronger check is wasmMemory.buffer.constructor === globalThis.SharedArrayBuffer with an Object.prototype.toString fallback.

Suggested change
if (Object.getPrototypeOf(wasmMemory.buffer).constructor.name === "SharedArrayBuffer") {
if (wasmMemory.buffer.constructor === globalThis.SharedArrayBuffer ||
Object.prototype.toString.call(wasmMemory.buffer) === "[object SharedArrayBuffer]") {

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Copilot AI Jul 3, 2025

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Wrap prototype access in optional chaining to avoid runtime errors if the prototype is null: Object.getPrototypeOf(wasmMemory.buffer)?.constructor?.name === 'SharedArrayBuffer'.

Suggested change
if (Object.getPrototypeOf(wasmMemory.buffer).constructor.name === "SharedArrayBuffer") {
if (Object.getPrototypeOf(wasmMemory.buffer)?.constructor?.name === "SharedArrayBuffer") {

Copilot uses AI. Check for mistakes.
// When the wasm memory is backed by a SharedArrayBuffer, growing the memory
// doesn't invalidate the data view by setting the byte length to 0. Instead,
// the data view points to an old buffer after growing the memory. So we have
Expand Down Expand Up @@ -796,8 +801,9 @@ class SwiftRuntime {
throw new Error("threadChannel is not set in options given to SwiftRuntime. Please set it to request transferring objects.");
}
const broker = getMessageBroker(this.options.threadChannel);
const sendingObjects = decodeObjectRefs(sending_objects, sending_objects_count, this.getDataView());
const transferringObjects = decodeObjectRefs(transferring_objects, transferring_objects_count, this.getDataView());
const dataView = this.getDataView();
const sendingObjects = decodeObjectRefs(sending_objects, sending_objects_count, dataView);
const transferringObjects = decodeObjectRefs(transferring_objects, transferring_objects_count, dataView);
broker.request({
type: "request",
data: {
Expand Down
8 changes: 7 additions & 1 deletion Runtime/src/index.ts
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Expand Up @@ -64,7 +64,13 @@ export class SwiftRuntime {
// Cache the DataView as it's not a cheap operation
let cachedDataView = new DataView(wasmMemory.buffer);
let cachedUint8Array = new Uint8Array(wasmMemory.buffer);
if (typeof SharedArrayBuffer !== "undefined" && wasmMemory.buffer instanceof SharedArrayBuffer) {

// Check the constructor name of the buffer to determine if it's backed by a SharedArrayBuffer.
// We can't reference SharedArrayBuffer directly here because:
// 1. It may not be available in the global scope if the context is not cross-origin isolated.
// 2. The underlying buffer may be still backed by SAB even if the context is not cross-origin
// isolated (e.g. localhost on Chrome on Android).
if (Object.getPrototypeOf(wasmMemory.buffer).constructor.name === "SharedArrayBuffer") {
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Relying on constructor.name can break if code is minified or prototypes are altered. Consider using a direct equality check when globalThis.SharedArrayBuffer is available (wasmMemory.buffer.constructor === globalThis.SharedArrayBuffer) or fall back to Object.prototype.toString.call(wasmMemory.buffer) === '[object SharedArrayBuffer]' for more robust detection.

Suggested change
if (Object.getPrototypeOf(wasmMemory.buffer).constructor.name === "SharedArrayBuffer") {
if (
(globalThis.SharedArrayBuffer && wasmMemory.buffer.constructor === globalThis.SharedArrayBuffer) ||
Object.prototype.toString.call(wasmMemory.buffer) === '[object SharedArrayBuffer]'
) {

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Copilot AI Jul 3, 2025

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Accessing Object.getPrototypeOf(...).constructor without checking for null/undefined can throw if buffer has a null prototype. Add optional chaining: Object.getPrototypeOf(wasmMemory.buffer)?.constructor?.name === 'SharedArrayBuffer'.

Suggested change
if (Object.getPrototypeOf(wasmMemory.buffer).constructor.name === "SharedArrayBuffer") {
if (Object.getPrototypeOf(wasmMemory.buffer)?.constructor?.name === "SharedArrayBuffer") {

Copilot uses AI. Check for mistakes.
// When the wasm memory is backed by a SharedArrayBuffer, growing the memory
// doesn't invalidate the data view by setting the byte length to 0. Instead,
// the data view points to an old buffer after growing the memory. So we have
Expand Down